Method for manufacturing semiconductor device and manufacturing apparatus of semiconductor device

ABSTRACT

A semiconductor device including an oxide semiconductor and an organic resin film is manufactured in the following manner. Heat treatment is performed on a first substrate provided with an organic resin film over a transistor including an oxide semiconductor in a reduced pressure atmosphere; handling of the first substrate is performed in an atmosphere containing moisture as little as possible in an inert gas (e.g., nitrogen) atmosphere with a dew point of lower than or equal to −60° C., preferably with a dew point of lower than or equal to −75° C. without exposing the first substrate after the heat treatment to the air; and then, the first substrate is bonded to a second substrate that serves as an opposite substrate.

This application is a continuation of copending U.S. application Ser.No. 15/276,194, filed on Sep. 26, 2016 which is a continuation of U.S.application Ser. No. 14/825,383, filed on Aug. 13, 2015 (now U.S. Pat.No. 9,460,940 issued Oct. 4, 2016) which is a continuation of U.S.application Ser. No. 14/048,376, filed on Oct. 8, 2013 (now U.S. Pat.No. 9,142,652 issued Sep. 22, 2015), which are all incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention disclosed in this specification and the likerelates to a method for manufacturing a semiconductor device and amanufacturing apparatus of the semiconductor device.

In this specification and the like, a semiconductor device refers to alltypes of devices which can function by utilizing semiconductorcharacteristics; an electro-optical device, an image display device, asemiconductor circuit, and an electronic device are all semiconductordevices.

2. Description of the Related Art

A technique for forming transistors using semiconductor thin filmsformed over a substrate having an insulating surface has been attractingattention. Such a transistor is applied to a wide range of electronicdevices such as an integrated circuit (IC) and an image display device(also simply referred to as a display device). A silicon-basedsemiconductor material is widely known as a material for a semiconductorthin film applicable to a transistor. As another material, an oxidesemiconductor has been attracting attention.

For example, a technique by which a transistor is formed using zincoxide or an In—Ga—Zn-based oxide semiconductor as an oxide semiconductoris disclosed (see Patent Documents 1 and 2).

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2007-123861

[Patent Document 2] Japanese Published Patent Application No. 2007-96055

SUMMARY OF THE INVENTION

However, in a semiconductor device including an oxide semiconductor, animpurity containing hydrogen, such as moisture, in the oxidesemiconductor might change the electric conductivity thereof such aphenomenon becomes a factor of a change in the electricalcharacteristics of a transistor using the oxide semiconductor.

In the semiconductor device, an organic resin film is used as aplanarization film which planarizes steps caused by transistors. Whilehaving an advantage that a preferable flat surface can be easily formed,the organic resin film easily adsorbs moisture. Thus, in the case wherethe organic resin film is used as a planarization film which covers atransistor including an oxide semiconductor, the electricalcharacteristics of the transistor might be changed by moisture absorbedin the organic resin film.

In view of the above problem, an object of one embodiment of the presentinvention is to provide a semiconductor device which includes an oxidesemiconductor and an organic resin film and has stable electricalcharacteristics, and a method for manufacturing thereof.

Further, another abject of one embodiment of the present invention is toprovide a manufacturing apparatus capable of manufacturing asemiconductor device which has stable electrical characteristics andhigh reliability.

In one embodiment of the present invention, a semiconductor device ismanufactured in the following manner. Heat treatment is performed on afirst substrate provided with an organic resin film over a transistorincluding an oxide semiconductor in a reduced pressure atmosphere;handling of the first substrate is performed in an atmosphere containingmoisture as little as possible (e.g., in an inert gas (e.g., nitrogen)atmosphere with a dew point of lower than or equal to −60° C.,preferably with a dew point of lower than or equal to −75° C., or in adry air atmosphere with a dew point of lower than or equal to −60° C.,preferably with a dew point of lower than or equal to −75° C.) withoutexposing the first substrate after the heat treatment to the air; andthen, the first substrate is bonded to a second substrate that serves asan opposite substrate.

Specifically, a semiconductor device is manufactured, by a manufacturingmethod below, for example.

One embodiment of the present invention is a method for manufacturing asemiconductor device which includes the steps of performing heattreatment in a reduced pressure atmosphere on a first substrate providedwith a transistor including an oxide semiconductor layer and an organicresin film provided over the transistor; applying a sealant to one ofthe first substrate and a second substrate which faces the firstsubstrate; disposing a surface of the first substrate over which thetransistor and the organic resin film are provided and the secondsubstrate facing each other, and bonding them to each other; and curingthe sealant. The steps from the heat treatment to curing of the sealantare performed in succession in an atmosphere with a dew point of lowerthan or equal to −60° C. without exposure to the air.

One embodiment of the present invention is a method for manufacturing asemiconductor device which includes the steps of performing heattreatment in a reduced pressure atmosphere on a first substrate providedwith a transistor including an oxide semiconductor layer and an organicresin film provided over the transistor; applying a sealant in a frameshape to one of the first substrate and a second substrate which facesthe first substrate, and dropping a liquid crystal inside the sealant ina frame shape; disposing a surface of the first substrate over which thetransistor and the organic resin film are provided and the secondsubstrate facing each other, and bonding them to each other; and curingthe sealant. The steps from the heat treatment to curing of the sealantare performed in succession in an atmosphere with a dew point of lowerthan or equal to −60° C. without exposure to the air.

One embodiment of the present invention is a method for manufacturing asemiconductor device which includes the steps of performing heattreatment in a reduced pressure atmosphere on a first substrate providedwith a transistor including an oxide semiconductor layer, an organicresin film provided over the transistor, and a light-emitting elementcontaining a light-emitting organic compound; applying a sealant to oneof the first substrate and a second substrate which faces the firstsubstrate; disposing a surface of the first substrate over which thetransistor and the organic resin film are provided and the secondsubstrate facing each other, and bonding them to each other; and curingthe sealant. The steps from the heat treatment to curing of the sealantare performed in succession in an atmosphere with a dew point of lowerthan or equal to −60° C. without exposure to the air.

In any one of the above methods for manufacturing a semiconductordevice, before bonding the first substrate and the second substrate toeach other, heat treatment is preferably performed on the secondsubstrate in a reduced pressure atmosphere.

In any one of the above methods for manufacturing a semiconductordevice, the steps from the heat treatment to curing of the sealant arepreferably performed in an inert gas atmosphere.

In any one of the above methods for manufacturing a semiconductordevice, bonding of the first substrate and the second substrate areperformed in a reduced pressure atmosphere. Specifically, the bonding ispreferably performed in an atmosphere at a pressure of 20 kPa to 0.1 Pa,more preferably 100 Pa to 1 Pa.

One embodiment of the present invention includes a manufacturingapparatus of a semiconductor device which is capable of performing theabove-described manufacturing steps. That is, another embodiment of thepresent invention is a manufacturing apparatus of a semiconductor devicewhich includes a heat treatment chamber for heating a substrate in areduced pressure atmosphere; an application chamber including a firstdispenser which applies a sealant and a second dispenser which drops aliquid crystal; a bonding chamber for bonding a pair of substrates, atleast one of which is heated in the heat treatment chamber, with thesealant, which is applied in the application chamber, providedtherebetween; a curing chamber for curing the sealant; and atransferring chamber for transferring a substrate between thetransferring chamber and each of the heat treatment chamber, theapplication chamber, the bonding chamber, and the curing chamber withoutexposure to the air. Atmospheres in the heat treatment chamber, theapplication chamber, the bonding chamber, the curing chamber, and thetransferring chamber are each controlled so as to have a dew point oflower than or equal to −60° C.

According to one embodiment of the present invention, a semiconductordevice which includes an oxide semiconductor and an organic resin filmand has stable electrical characteristics, and a method formanufacturing thereof can be provided.

According to one embodiment of the present invention, a manufacturingapparatus with which it is possible to manufacture a semiconductordevice having stable electrical characteristics and high reliability canbe provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a manufacturing apparatus of asemiconductor device.

FIGS. 2A to 2D each illustrate one embodiment of a treatment chamber ofa manufacturing apparatus.

FIG. 3 illustrates one embodiment of a manufacturing apparatus of asemiconductor device.

FIG. 4 is a conceptual diagram of a structure of a display device.

FIG. 5 is a graph showing the intensities of gas molecules having amass-to-charge ratio (m/z) of 18 and being desorbed from circuit boardseach including an organic resin film.

FIG. 6 is a graph showing the intensities of gas molecules having amass-to-charge ratio (m/z) of 18 and being desorbed from circuit boardseach not including an organic resin film.

FIGS. 7A to 7E are perspective views illustrating manufacturing steps ofa semiconductor device.

FIGS. 8A to 8C each illustrate a structural example of a display deviceof one embodiment.

FIGS. 9A to 9C each illustrate a structural example of a display deviceprovided with a touch sensor of one embodiment of the present invention.

FIGS. 10A to 10F each illustrate an electronic device of one embodimentof the present invention.

FIG. 11 is a graph showing a change in an operating margin width withrespect to operation time of a scan line driver circuit (subjected toheat treatment).

FIG. 12 is a graph showing a change in an operating margin width withrespect to operation time of a scan line driver circuit (not subjectedto heat treatment).

FIG. 13 illustrates one embodiment of a manufacturing apparatus that isused in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that thepresent invention is not limited to the description below and it iseasily understood by those skilled in the art that the mode and detailscan be changed in various ways. Therefore, the invention should not beconstrued as being limited to the description in the followingembodiments.

Note that in structures of the present invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals throughout different drawings, and descriptionthereof is not repeated.

Note that in each drawing described in this specification, the size, thefilm thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such scales.

Note that the ordinal numbers such as “first” and “second” in thisspecification and the like are used for convenience and do not denotethe order of steps or the stacking order of layers. In addition, theordinal numbers in this specification do not denote particular nameswhich specify the present invention.

In this specification, a term “parallel” indicates that two straightlines are provided so that the angle formed therebetween is greater thanor equal to −10° and less than or equal to 10°, and accordingly alsoincludes the case where the angle is greater than or equal to −5° andless than or equal to 5°. In addition, a term “perpendicular” indicatesthat two straight lines are provided so that the angle formedtherebetween is greater than or equal to 80° and less than or equal to100°, and accordingly includes the case where the angle is greater thanor equal to 85° and less than or equal to 95°.

In this specification, the trigonal and rhombohedral crystal systems areincluded in the hexagonal crystal system.

Embodiment 1

In this embodiment, a manufacturing apparatus and a method formanufacturing a semiconductor device using the manufacturing apparatusaccording to one embodiment of the present invention are described withreference to FIG. 1, FIGS. 2A to 2D, and FIG. 3.

<1-1. Structure 1 of Manufacturing Apparatus>

FIG. 1 illustrates an example of a plan view of a manufacturingapparatus 400. The manufacturing apparatus 400 in FIG. 1 is amanufacturing apparatus for bonding an element substrate (hereinafteralso referred to as a first substrate) provided with a transistor and anopposite substrate (hereinafter also referred to as a second substrate)(a cell process).

The manufacturing apparatus 400 illustrated in FIG. 1 includes a firstheat treatment chamber 50A, a second heat treatment chamber 50B, anapplication chamber 54 including a dispenser for applying a sealant, abonding chamber 56 in which a pair of substrates is bonded with thesealant, which is applied in the application chamber 54, providedtherebetween, a curing chamber 58 for curing the sealant, and atransferring chamber 52 for transferring a substrate between thetreatment chambers. In addition, an unloading chamber 60 for unloadingthe bonded substrates may be included as a component of themanufacturing apparatus 400.

In the manufacturing apparatus 400 in FIG. 1, the first heat treatmentchamber 50A, the second heat treatment chamber 50B, the applicationchamber 54, the bonding chamber 56, the curing chamber 58, the unloadingchamber 60, and the transferring chamber 52 are controlled so as tocontain moisture as little as possible. For example, the inside of themanufacturing apparatus 400 is controlled to have an inert gasatmosphere with a dew point of −60° C. or lower, preferably −75° C. orlower (a dry nitrogen gas atmosphere or a dry argon gas atmosphere), ora dry air atmosphere with a dew point of −60° C. or lower, preferably−75° C. or lower.

Further, the substrates (the first substrate and the second substrate)are processed in succession in each treatment chamber without beingexposed to the air after being carried into the first heat treatmentchamber 50A or the second heat treatment chamber 50B and before beingcarried out from the unloading chamber 60. Note that the arrows in FIG.1 indicate the substrate carry-in/out directions.

<1-2. Structure of Each Treatment Chamber>

An example of a structure of a treatment chamber included in themanufacturing apparatus 400 is described with reference to FIGS. 2A to2D.

<1-2-1. Heat Treatment Chamber>

The first heat treatment chamber 50A is a treatment chamber in whichsubstrates carried into the manufacturing apparatus 400 are heated in areduced-pressure atmosphere (see FIG. 2A). In the first heat treatmentchamber 50A, with the use of a heater 412, heat treatment is performedon the substrates in a cassette 411 capable of holding a plurality ofsubstrates, while the cassette 411 is moved up and down by an elevator417.

When the heat treatment is performed, the atmosphere is controlled tohave a pressure of 1 Pa or less, preferably 10⁻⁴ Pa or less and a dewpoint of −60° C. or less, preferably −80° C. or less in such a mannerthat the air in the treatment chamber is exhausted via an exhaust port414 so that the pressure in the treatment chamber is reduced, and aninert gas such as nitrogen or argon or a dry air is introduced from agas introducing port 415.

Note that in FIG. 2A, an example in which the cassette 411 is moved upand down by the elevator 417 that is provided on the lower side in thetreatment chamber is illustrated; however, this embodiment is notlimited to this. For example the elevator 417 may be provided on theupper side in the treatment chamber. Further, in FIG. 2A, an example inwhich the gas introducing port 415 and the exhaust port 414 are providedon the upper side in the treatment chamber is illustrated; however, thepositions of the gas introducing port 415 and the exhaust port 414 arenot limited to them.

The second heat treatment chamber 50B has a structure similar to that ofthe first heat treatment chamber 50A. Note that the manufacturingapparatus 400 in FIG. 1 has two heat treatment chambers as an example;however, this embodiment is not limited to this structure. Themanufacturing apparatus 400 has at least one heat treatment chamber, ormay have three or more heat treatment chambers.

<1-2-2. Transferring Chamber>

The transferring chamber 52 is a treatment chamber through which asubstrate is transferred to each treatment chamber (see FIG. 2A). When asubstrate is transferred, a shutter 405 provided between thetransferring chamber and each treatment chamber is opened, and thesubstrate is moved on a sheet-by-sheet basis by a transferring arm 418.

The inside of each treatment chamber provided in the manufacturingapparatus 400 is controlled to have an atmosphere with a dew point of−60° C. or less, preferably −80° C. or less using the gas introducingport 415 and a check valve 416. When the treatment chamber has theexhaust port 414, the check valve 416 is not necessarily provided.

<1-2-3. Application Chamber>

The application chamber 54 is a treatment chamber in which a sealant isapplied to a substrate (see FIG. 2B). In the application chamber 54,after the substrate is mounted on a stage 421, a dispenser 420 and thestage 421 are relatively moved, whereby the sealant is applied to apredetermined position on the substrate.

In FIG. 2B, the case where the stage 421 is moved is illustrated;however, this embodiment is not limited to this. The dispenser 420 maybe moved; alternatively, both the stage 421 and the dispenser 420 may bemoved. Further, a plurality of dispensers 420 may be provided, and adispenser capable of applying a material (e.g., a liquid crystal, adrying agent, or an anisotropic conductive resin, or the like) otherthan the sealant may be provided in addition to the dispenser forapplying the sealant.

<1-2-4. Bonding Chamber>

The bonding chamber 56 is a treatment chamber in which the firstsubstrate and the second chamber are bonded to each other (see FIG. 2C).The substrate to which the sealant is applied in the application chamber54 is mounted on a first stage 422 so as to face a substrate arranged ona second stage 423. When bonding is performed, after the first stage 422and/or the second stage 423 is moved up/down so that the pair ofsubstrates is brought close to each other, barriers 425 are moved so asto form a closed space. Subsequently, the air inside the closed space isexhausted via the exhaust port 414 so that the pressure in the closedspace is reduced. The bonding is performed in an atmosphere at apressure of 20 kPa to 0.1 Pa, more preferably 100 Pa to 1 Pa.

Note that the barriers 425 are not necessarily provided. However, theprovision of the barriers 425 is preferable because the volume of theclosed space that has a reduced pressure atmosphere can be reducedcompared with the case where the whole bonding chamber 56 has a reducedpressure atmosphere and thus the productivity can be improved.

<1-2-5. Curing Chamber>

The curing chamber 58 is a treatment chamber in which the sealant afterthe bonding is cured (see FIG. 2D). For example, in the case of using anultraviolet curable resin as the sealant, the sealant can be cured usinga UV lamp 424 in the curing chamber 58.

When the pair of substrates is transferred from the bonding chamber 56to the curing chamber 58, it is preferable that the substrates aretemporarily bonded to each other in the bonding chamber 56 so thatpositional misalignment of the pair of substrates is prevented.

<1-3. Cell Process>

A cell process using the manufacturing apparatus 400 illustrated in FIG.1 and FIGS. 2A to 2D are described below.

First, after being carried into the heat treatment chamber 50A, thefirst substrate is subjected to heat treatment in a reduced pressureatmosphere. Next, in the application chamber 54, the sealant is appliedto either one of the first substrate and the second substrate after theheat treatment. After that, the first substrate and the second substrateare disposed so as to face each other and bonded to each other in thebonding chamber 56; then, the sealant is cured in the curing chamber 58.The pair of substrates with the sealant cured is carried out from theunloading chamber 60. In this manner, a semiconductor device of thisembodiment can be manufactured. In the manufacturing apparatus 400described in this embodiment, the substrates are moved between thetreatment chambers via the transfer chamber 52, so that the cell processcan be performed without exposure to the air.

<1-4. Structure 2 of Manufacturing Apparatus>

FIG. 3 illustrates another structural example of the manufacturingapparatus.

FIG. 3 is an example in which a plurality of treatment chambers isarranged on a substantially straight line. In a manufacturing apparatus402 illustrated in FIG. 3, without arrangement of the transfer chamber52 at the center, a substrate can be transferred to treatment chambersin succession using a transfer mechanism or the like arranged in eachtreatment chamber, for example. The floor area (so-called footprint) ofthe apparatus can be reduced with the structure in FIG. 3.

Note that the structure of the manufacturing apparatus is not limited tothis, and can be properly changed depending on the layout of a cleanroom, or the like.

The structures and methods described in this embodiment can be combinedas appropriate with any of the methods and structures described in theother embodiments.

Embodiment 2

In this embodiment, a method for manufacturing a semiconductor device(also referred to as a display device) having a display function usingthe manufacturing apparatus described in Embodiment 1 is described.

<2-1. Structure of Display Device>

FIG. 4 shows a conceptual diagram of the structure of a display device.In the display device, a first substrate 100 provided with a transistor302 and a second substrate 200 are bonded to each other with a displayelement 306 provided therebetween. As the display element 306, forexample, a liquid crystal element, a light-emitting element, or the likecan be used.

In this embodiment, a transistor including an oxide semiconductor filmin a channel formation region is used as the transistor 302. Atransistor with a bottom gate structure is illustrated in FIG. 4 as anexample; however, the structure is not limited to this, and a transistorwith a top gate structure may be employed.

An oxide semiconductor is a semiconductor material whose band gap can bewider than that of silicon and whose intrinsic carrier density can belower than that of silicon. Thus, the off-state current of thetransistor 302 including an oxide semiconductor film can be extremelylow compared with a transistor including an amorphous silicon film or apolycrystalline silicon film. Therefore, reduction in power consumptionof the display device can be achieved by forming a backplane (a circuitboard) of a liquid crystal display device or an organic EL displaydevice using a transistor including an oxide semiconductor film.

As a base film of the display element 306, an organic resin film 304 ispreferably formed. For example, in the case of using a liquid crystalelement as the display element 306, an alignment defect of liquidcrystal molecules can be prevented by provision of the organic resinfilm 304 functioning as a planarization film. Further, in the case ofusing a light-emitting element containing an organic compound as thedisplay element 306, disconnection of a light-emitting layer caused dueto its small thickness can be prevented by provision of the organicresin film 304 functioning as a planarization film.

While having advantages that a preferable flat surface is easily formedand the relative permittivity is lower than that of an inorganicinsulating film, an organic resin film easily adsorbs moisture.Meanwhile, in an oxide semiconductor, hydrogen becomes a supply sourceof carriers, and a donor is generated at a level close to the conductionband (a shallow level) to lower the resistance (make the oxidesemiconductor an n-type oxide semiconductor) when hydrogen is containedin the oxide semiconductor. Thus, moisture is an impurity for the oxidesemiconductor, and is a factor of a change in the electricalcharacteristics of a transistor.

<2-2. Characteristics of Organic Resin Film>

Results of examining the amount of moisture released from a circuitboard including an organic resin film by thermal desorption spectroscopy(TDS) are described below.

First, seven circuit boards A to G which were used for the TDS aredescribed.

The circuit boards A to D are each a substrate over which an organicresin film is formed as a planarization film and an alignment film of aliquid crystal element is formed over the organic resin film. Thecircuit boards A to D were formed in the same process up to andincluding formation of the alignment film. Further, in each of thecircuit boards A to D, a 3-μm-thick organic resin film including anacrylic resin is formed between a transistor and a pixel electrode.

The circuit board A was not subjected to heat treatment after formationof the alignment film. The circuit board B was subjected to heattreatment at 160° C. for one hour in a reduced pressure atmosphere ofabout 10⁻⁵ Pa after formation of the alignment film. The circuit board Cwas subjected to heat treatment at 150° C. for six hours in an airatmosphere after formation of the alignment film. The circuit board Dwas subjected to heat treatment at 160° C. for one hour in a reducedpressure atmosphere of about 10⁻⁵ Pa and then was exposed to an airatmosphere for ten minutes.

The circuit boards E to G were formed in the same process up to andincluding formation of the alignment film. The circuit boards E to Geach have a structure in which an organic resin film including anacrylic resin is not provided between a transistor and a pixel electrodeand a pixel electrode is provided over an inorganic insulating film thatcovers the transistor. The circuit board E was not subjected to heattreatment after formation of the alignment film. The circuit board F wassubjected to heat treatment at 160° C. for one hour in a reducedpressure atmosphere of about 10⁻⁵ Pa after formation of the alignmentfilm. The circuit board G was subjected to heat treatment at 150° C. forsix hours in an air atmosphere after formation of the alignment film.

In the TDS, the temperature of each board was raised from 60° C. to 230°C. at a speed of 20° C. per minute and the number of desorbed gasmolecules having a mass-to-charge ratio (m/z) of 18 was measured. Notethat it is expected that the gas molecules having a mass-to-charge ratio(m/z) of 18 mainly include water. Further, an atmospheric pressure atthe beginning of the measurement in a measurement chamber in which thecircuit board was placed was 1.2×10⁻⁷ Pa.

FIG. 5 shows the intensities of gas molecules having a mass-to-chargeratio (m/z) of 18 and being desorbed from each of the circuit boards Ato D, which were obtained by TDS.

The circuit board A which was not subjected to heat treatment has a peakshowing desorption of water at a substrate temperature around 90° C. Onthe other hand, unlike the circuit board A, the circuit board B whichwas subjected to heat treatment in a reduced pressure atmosphere doesnot have a peak showing desorption of water at a substrate temperaturearound 90° C.

When the circuit board B which was subjected to heat treatment in areduced pressure atmosphere is compared with the circuit board C whichwas subjected to heat treatment in an air atmosphere, the circuit boardC has higher intensity showing desorption of water than the circuitboard B at substrate temperatures of 160° C. or less. Thus, it isexpected that the amount of water included in each film included in thecircuit board B which was subjected to heat treatment in a reducedpressure atmosphere is smaller than that in the circuit board C whichwas subjected to heat treatment in an air atmosphere.

Further, the circuit board D which was exposed to an air atmosphereafter heat treatment in a reduced pressure atmosphere has a peak showingdesorption of water at a substrate temperature around 80° C. When thecircuit board B which was subjected to heat treatment in a reducedpressure atmosphere is compared with the circuit board D which wasexposed to an air atmosphere after the heat treatment in a reducedpressure atmosphere, it is expected that the amount of water included ineach film included in the circuit board D is larger than that in thecircuit board B.

FIG. 6 shows the intensities of gas molecules having a mass-to-chargeratio (m/z) of 18 and being desorbed from each of the circuit boards Eto G which were obtained by TDS.

When the intensity showing desorption of water of the circuit board Aincluding the organic resin film, which is shown in FIG. 5, is comparedwith that of the circuit board E not including the organic resin film,which is shown in FIG. 6, it is found that the intensity of the circuitboard A is higher than that of the circuit board E in all thetemperature ranges. Thus, as for the circuit boards A and E each ofwhich was not subjected to heat treatment after formation of thealignment film, it can be considered that more water is desorbed fromthe circuit board A including the organic resin film and that differencein the amount of desorbed water is caused by water included in theorganic resin film.

When the intensity of the circuit board C including the organic resinfilm, which is shown in FIG. 5, is compared with that of the circuitboard G not including the organic resin film, which is shown in FIG. 6,it is found that the intensity of the circuit board C is higher thanthat of the circuit board G in all the temperature ranges. Thus, as forthe circuit boards C and G each of which was subjected to heat treatmentin an air atmosphere after formation of the alignment film, it can beconsidered that more water is desorbed from the circuit board Cincluding the organic resin film and that the difference in the amountof desorbed water is caused by water included in the organic resin film.

Further, when the intensity showing desorption of water of the circuitboard B including the organic resin film, which is shown in FIG. 5, iscompared with that of the circuit board F not including the organicresin film, which is shown in FIG. 6, there are no significantdifference in the intensities at temperatures of 100° C. or less, andthe intensity of the circuit board B becomes higher when the temperatureexceeds 100° C. Thus, as for the circuit boards B and F each of whichwas subjected to heat treatment in a reduced pressure atmosphere afterformation of the alignment film, it can be considered that more waterare desorbed from the circuit board B including the organic resin filmand that the difference in the amount of desorbed water is caused bywater included in the organic resin film. However, as for the circuitboards B and F each of which was subjected to heat treatment in areduced pressure atmosphere, the difference in the amount of releasedwater is smaller than that in the case of the circuit boards A and E andthat in the case of the circuit boards C and G. Accordingly, it isconsidered that water included in the organic resin film is effectivelydesorbed by heat treatment in a reduced pressure atmosphere comparedwith the case where heat treatment is not performed or the case whereheat treatment is performed in an air atmosphere.

The above-described results of the TDS show that the display devicemanufactured using a manufacturing apparatus of one embodiment of thepresent invention, in which a display element can be sealed betweensubstrates without being exposed to the air (e.g., in a nitrogenatmosphere) after heat treatment at 160° C. in a reduced pressureatmosphere, contains little water in the organic resin film.

<2-3. Method for Manufacturing Display Device>

A method for manufacturing a semiconductor device using themanufacturing apparatus 400 is described below with reference to FIGS.7A to 7E. In this embodiment, description is made below on a case wherea liquid crystal display panel is manufactured as an example of adisplay panel.

In this embodiment, a method for manufacturing one liquid crystaldisplay device from a pair of substrates is shown; however, withoutlimitation thereto, this embodiment can also be applied to the casewhere a plurality of liquid crystal display devices is manufactured overa large-sized substrate (obtaining a plurality of panels).

<2-3-1. Heat Treatment>

First, the first substrate 100 provided with a transistor and aplanarization film over the transistor is carried into the first heattreatment chamber 50A, and is subjected to heat treatment in a reducedpressure atmosphere (see FIG. 7A).

In this embodiment, as the transistor provided over the first substrate100, a transistor including an oxide semiconductor is used. Further, asthe planarization film, an organic resin film is used.

Heat treatment is performed on the first substrate 100 provided with theorganic resin film over the transistor including an oxide semiconductor,whereby moisture is desorbed (dehydrated) from the organic resin filmand impurities such as moisture or hydrogen can be prevented fromentering the oxide semiconductor. Further, the heat treatment ispreferably performed in a reduced pressure atmosphere because not onlymoisture (adsorbed water) adsorbed to a surface of the organic resinfilm but also moisture in the organic resin film can be dehydrated.

Further, when an alignment film is formed over the first substrate 100,the heat treatment is preferably performed in a reduced pressureatmosphere because impurities such as water or hydrogen can be desorbedalso from the alignment film. In this embodiment, the first substrate100 provided with the alignment film which has been subjected to rubbingtreatment is carried into the first heat treatment chamber 50A.

The heating temperature is preferably 100° C. or higher, more preferably150° C. or higher. The upper limit of the heating temperature variesdepending on materials used for the organic resin film. In the casewhere an acrylic-based resin is used, the upper limit of the heatingtemperature is about 180° C. to 250° C., and in the case where apolyimide-based resin is used, the upper limit of the heatingtemperature is about 250° C. to 300° C. However, the heating temperaturemay be set as appropriate in consideration of the material to be usedand the degree of vacuum at the time of reducing pressure.

Further, the reduced pressure atmosphere has a pressure lower than theatmospheric pressure, preferably lower than or equal to 1 Pa, morepreferably lower than or equal to 10⁻⁴ Pa. Here, Pa represents thedegree of vacuum; that is, “lower than or equal to” means the directionin which the degree of vacuum is higher.

In this embodiment, the first substrate 100 is subjected to the heattreatment at 160° C. for one hour in an atmosphere where the pressure isreduced to 10⁻⁵ Pa.

The first substrate 100 after the heat treatment is transferred to thebonding chamber 56 via the transfer chamber 52. The movement ofsubstrates via the transfer chamber 52 is successively performed withoutbeing exposed to the air.

Further, the second substrate 200 is carried into the second heattreatment chamber 50B and is subjected to heat treatment in a reducedpressure atmosphere (see FIG. 7B). Note that the heat treatment on thesecond substrate 200 may precede the heat treatment on the firstsubstrate 100 and the second substrate 200 may be kept in a vacuum.Further, the condition of the heat treatment on the second substrate 200can be similar to that on the first substrate 100.

Note that when the second substrate 200 does not include an organicresin film, the heat treatment is not necessarily performed on thesecond substrate 200. However, the heat treatment is preferablyperformed on the second substrate 200 in a reduced pressure atmospherebecause water adsorbed to a surface of the second substrate 200 can bereleased by the heat treatment and impurities such as moisture in aregion that is sealed in a later step can be reduced.

Further, when an alignment film is formed over the second substrate 200,the heat treatment is preferably performed on the second substrate 200in a reduced pressure atmosphere because impurities such as water ormoisture can be released also from the alignment film.

In this embodiment, the second substrate 200 provided with an alignmentfilm which has been subjected to rubbing treatment is carried into thesecond heat treatment chamber 50B and is subjected to heat treatment at160° C. for one hour in an atmosphere where the pressure is reduced to10⁻⁵ Pa.

In FIGS. 7A to 7E, an example of the case where the first substrate 100and the second substrate 200 are subjected to heat treatment inrespective heat treatment chambers is illustrated; however, thisembodiment is not limited to this. The first substrate 100 and thesecond substrate 200 may be subjected to heat treatment in the same heattreatment chamber; alternatively, a structure may be employed in which aplurality of the first substrate 100 or a plurality of the secondsubstrate 200 is subjected to heat treatment in a plurality of heattreatment chambers. If the manufacturing apparatus 400 has a pluralityof heat treatment chambers, the semiconductor device can be efficientlymanufactured. Further, it is preferable that batch processing can beperformed in the first heat treatment chamber 50A and the second heattreatment chamber 50B because heat treatment can be performed on aplurality of substrates at the same time.

<2-3-2. Application of Sealant and Drop of Liquid Crystal>

The second substrate 200 after the heat treatment is transferred to theapplication chamber 54 via the transfer chamber 52.

In the application chamber 54, a sealant 202 is applied in a frame shapeto the second substrate 200 after the heat treatment, and a liquidcrystal 204 is dropped inside the sealant in a frame shape (see FIG.7C).

When a plurality of panels is obtained from one substrate, the sealantmay be applied in a plurality frame shapes.

As the sealant 202, a photocurable resin, a thermosetting resin, aphotocurable and thermosetting resin, or the like is preferably used.For example, an acrylic-based resin, an epoxy-based resin, anacrylate-based (urethane acrylate) resin, an amine-based resin, or aresin in which an acrylic-based resin and an epoxy-based resin are mixedcan be used. Further, a photopolymerization initiator (typically, anultraviolet light polymerization initiator), a thermosetting agent, afiller, or a coupling agent may be included in the sealant 202. Notethat a photocurable resin is cured by light irradiation and athermosetting resin is cured by heat treatment. A photocurable andthermosetting resin is temporarily cured (pre-cured) by lightirradiation and then fully cured by heat treatment.

Moreover, the sealant 202 may be formed in a frame shape (closed-loopshape). In FIG. 7C, the case where the sealant 202 is formed in arectangular frame shape is described. Note that the shape of the sealant202 is not limited to the rectangular frame shape, and the sealant 202may be formed in a circular frame shape, an elliptical frame shape, apolygonal frame shape other than the rectangular frame shape, or thelike. Alternatively, the sealant 202 may be formed so as to form doubleor more frames, in that case, materials for the sealants of the innerframe and the outer frame may be different.

For the liquid crystal 204, a low-molecular liquid crystal, aferroelectric liquid crystal, an anti-ferroelectric liquid crystal, orthe like can be used. Further, for a liquid crystal material, a liquidcrystal composition in which a chiral agent, a polymerizable monomer,and a polymerization initiator are mixed may be used.

Note that FIG. 7C illustrates a case where one droplet of the liquidcrystal 204 is dropped inside the sealant 202. However, this embodimentis not limited to such a manner, and appropriate amounts of the liquidcrystal material may be dropped at appropriate places on the inner sidethan the sealant 202 in a frame shape.

Further, a third dispenser that is used for dropping an anisotropicconductive resin for electrical connection with a flexible printedcircuit (FPC) may be provided in the application chamber 54.

Note that in this embodiment, an example of the case where the liquidcrystal display device is manufactured using the manufacturing apparatus400 is described; however, this embodiment is not limited to this. Forexample, an electroluminescence (EL) display device may be manufacturedusing the manufacturing apparatus 400 in such a manner that a firstsubstrate that is provided with a transistor including an oxidesemiconductor layer, an organic resin film provided over the transistor,and a light-emitting element including a light-emitting organiccompound, and a second substrate are bonded to each other. In that case,in the application chamber 54, a sealant for solid sealing can beapplied. Instead of a liquid crystal, a drying agent may be dropped orapplied.

<2-3-3. Bonding>

After the liquid crystal 204 is dropped, the second substrate 200 istransferred to the bonding chamber 56 via the transfer chamber 52.

In the bonding chamber 56, a surface of the first substrate 100 overwhich the transistor and the organic resin film are provided and thesecond substrate 200 are disposed to face each other, and the firstsubstrate 100 and the second substrate 200 are bonded to each other (seeFIG. 7D).

When the first substrate 100 and the second substrate 200 are bonded toeach other, the dropped liquid crystal 204 spreads over inside the frameof the sealant 202; thus, a liquid crystal layer is formed. Note thatdepending on the viscosity of the dropped liquid crystal, the liquidcrystal layer does not spread over the entire surface inside the frameof the sealant 202 (the liquid crystal layer is not in contact with thesealant 202) at the stage of bonding the first substrate 100 and thesecond substrate 200 in some cases.

The first substrate 100 and the second substrate 200 are bonded to eachother in a reduced pressure atmosphere. This is because when thesubstrates are bonded to each other in a reduced pressure atmosphere,even if the substrates are exposed to the atmospheric pressure after thebonding, the inside of the frame of the sealant 202 can be kept in areduced pressure and the liquid crystal can finally spread to be incontact with the sealant 202. Further, this is because the sealant isprevented from tearing due to pressure caused by compression of a gasinside the frame of the sealant 202 at the time of sealing. The reducedpressure atmosphere preferably has a pressure lower than the atmosphericpressure, more preferably 100 Pa or lower, for example.

The bonding chamber 56 preferably has a lower vacuum state than each ofthe first heat treatment chamber 50A and the second heat treatmentchamber 50B. For example, the atmosphere in the bonding chamber 56 ispreferably set at a pressure of 20 kPa to 0.1 Pa, more preferably 100 Pato 1 Pa.

Note that after the sealant 202 is formed over the second substrate 200or after the first substrate 100 and the second substrate 200 are bondedto each other, the sealant 202 may be temporarily cured through lightirradiation or heat treatment. Note that instead of using the sealant202 in a frame shape, a sealant for temporary bonding substrates may beapplied to an edge portion of the substrate 200; in that case, thesealant for temporary bonding may be temporarily cured.

The sealant 202 is temporarily cured, so that the sealant 202 and thesubstrates (the first substrate 100 and the second substrate 200) arefirmly bonded to each other and positional misalignment of the top andbottom substrates can be prevented.

Further, FIGS. 7A to 7E illustrate the case where the sealant 202 andthe liquid crystal 204 are provided on the second substrate 200 side;however, the sealant 202 and the liquid crystal 204 may be provided onthe first substrate 100 side.

<2-3-4. Curing of Sealant>

After being bonded to each other in the bonding chamber 56, the firstsubstrate 100 and the second substrate 200 are transferred to the curingchamber 58 via the transfer chamber 52; then, cure treatment of thesealant 202 is performed (see FIG. 7E). Note that the cure treatment isperformed in an atmospheric pressure atmosphere.

The cure treatment may be set as appropriate in accordance with thematerial of the sealant. For example, when a thermosetting resin is usedfor the sealant 202, heat treatment is performed to cure the sealant202. Alternatively, when a photocurable resin is used for the sealant202, the sealant 202 is cured by irradiating the photocurable resin withlight having a wavelength with which the photocurable resin reacts.

Through the above steps, the liquid crystal display device 300 of thisembodiment can be manufactured. The manufactured liquid crystal displaydevice 300 is carried out from the unloading chamber 60 illustrated inFIG. 1.

As described above, using a manufacturing apparatus of one embodiment ofthe present invention, the first substrate 100, or the first substrate100 and the second substrate 200 is/are heated in a reduced pressureatmosphere, so that water can be removed from the organic resin filmprovided over the substrate. A compound including hydrogen such as wateris an impurity which imparts n-type conductivity to an oxidesemiconductor, which becomes a factor of a change in the electricalcharacteristics of a transistor using an oxide semiconductor. Thus, theconcentration of water to be mixed in the display device is decreased,whereby reliability of the transistor can be improved.

Further, moisture is easily adsorbed to the organic resin film. Thus,even if water is removed by heat treatment, entry of water is likely tooccur when the organic resin film is exposed to the air. However, in themanufacturing apparatus of this embodiment, the first substrate 100 andthe second substrate 200 are bonded to each other without being exposedto the air after water is removed by the heat treatment. Accordingly,entry of impurities such as water into the display device can besuppressed. Therefore, a highly reliable semiconductor device can beprovided.

The methods and structures described in this embodiment can be combinedas appropriate with any of the methods and structures described in theother embodiments.

Embodiment 3

An example of an oxide semiconductor which is preferably used for theregion in the transistor where a channel is formed which is exemplifiedin the above embodiment is described below.

An oxide semiconductor has a wide energy gap of 3.0 eV or more. Atransistor including an oxide semiconductor film obtained by processingof the oxide semiconductor in an appropriate condition and a sufficientreduction in carrier density of the oxide semiconductor can have muchlower leakage current between a source and a drain in an off state(off-state current) than a conventional transistor including silicon.

An applicable oxide semiconductor preferably contains at least indium(In) or zinc (Zn). In particular, In and Zn are preferably contained. Inaddition, as a stabilizer for reducing a change in the electricalcharacteristics of a transistor using the oxide semiconductor, one ormore elements selected from gallium (Ga), tin (Sn), hafnium (Hf),zirconium (Zr), titanium (Ti), scandium (Sc), yttrium (Y), and alanthanoid (such as cerium (Ce), neodymium (Nd), or gadolinium (Gd)) ispreferably contained.

As the oxide semiconductor, for example, any of the following can beused: indium oxide, tin oxide, zinc oxide, an In—Zn-based oxide, aSn—Zn-based oxide, an Al—Zn-based oxide, a Zn—Mg-based oxide, aSn—Mg-based oxide, an In—Mg-based oxide, an In—Ga-based oxide, anIn—Ga—Zn-based oxide (also referred to as IGZO), an In—Al—Zn-basedoxide, an In—Sn—Zn-based oxide, a Sn—Ga—Zn-based oxide, anAl—Ga—Zn-based oxide, a Sn—Al—Zn-based oxide, an In—Hf—Zn-based oxide,an In—Zr—Zn-based oxide, an In—Ti—Zn-based oxide, an In—Sc—Zn-basedoxide, an In—Y—Zn-based oxide, an In—La—Zn-based oxide, anIn—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide,an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-basedoxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, anIn—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide,an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or anIn—Hf—Al—Zn-based oxide.

Here, an “In—Ga—Zn-based oxide” means an oxide containing In, Ga, and Znas its main components and there is no particular limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain a metal elementother than the In, Ga, and Zn.

Alternatively, a material represented by InMO₃(ZnO)_(m)(m>0 issatisfied) may be used as an oxide semiconductor. Note that M representsone or more metal elements selected from Ga, Fe, Mn, and Co, or theabove-described element as a stabilizer. Alternatively, as the oxidesemiconductor, a material expressed by a chemical formula,In₂SnO₅(ZnO)_(n)(n>0, n is an integer) may be used.

For example, In—Ga—Zn-based oxide with an atomic ratio whereIn:Ga:Zn=1:1:1, In:Ga:Zn=3:1:2, or In:Ga:Zn=2:1:3, or an oxide whosecomposition is in the neighborhood of the above compositions can beused.

The oxide semiconductor film may be either single crystal ornon-single-crystal. In the latter case, the oxide semiconductor film maybe any of an amorphous oxide semiconductor film, a microcrystallineoxide semiconductor film, a polycrystalline oxide semiconductor film,and a c-axis aligned crystalline oxide semiconductor (CAAC-OS) film. Theoxide semiconductor film is preferably a CAAC-OS film.

A structure of an oxide semiconductor film is described below.

The amorphous oxide semiconductor film has disordered atomic arrangementand no crystalline component. A typical example thereof is an oxidesemiconductor film in which no crystal part exists even in a microscopicregion, and the whole of the film is amorphous.

The microcrystalline oxide semiconductor film includes a microcrystal(also referred to as nanocrystal) with a size greater than or equal to 1nm and less than 10 nm, for example. Thus, the microcrystalline oxidesemiconductor film has a higher degree of atomic order than theamorphous oxide semiconductor film. Hence, the density of defect statesof the microcrystalline oxide semiconductor film is lower than that ofthe amorphous oxide semiconductor film.

The CAAC-OS film is one of oxide semiconductor films including aplurality of crystal parts, and most of the crystal parts each fitinside a cube whose one side is less than 100 nm. Thus, there is a casewhere a crystal part included in the CAAC-OS film fits a cube whose oneside is less than 10 nm, less than 5 nm, or less than 3 nm. The densityof defect states of the CAAC-OS film is lower than that of themicrocrystalline oxide semiconductor film. The CAAC-OS film is describedin detail below.

In a transmission electron microscope (TEM) image of the CAAC-OS film, aboundary between crystal parts, that is, a grain boundary is not clearlyobserved. Thus, in the CAAC-OS film, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

According to the TEM image of the CAAC-OS film observed in a directionsubstantially parallel to a sample surface (cross-sectional TEM image),metal atoms are arranged in a layered manner in the crystal parts. Eachmetal atom layer has a morphology reflected by a surface over which theCAAC-OS film is formed (hereinafter, a surface over which the CAAC-OSfilm is formed is referred to as a formation surface) or a top surfaceof the CAAC-OS film, and is arranged in parallel to the formationsurface or the top surface of the CAAC-OS film.

On the other hand, according to the TEM image of the CAAC-OS filmobserved in a direction substantially perpendicular to the samplesurface (plan TEM image), metal atoms are arranged in a triangular orhexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

From the results of the cross-sectional TEM image and the plan TEMimage, alignment is found in the crystal parts in the CAAC-OS film.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus. For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently when the diffraction angle (2θ) is around 31°.This peak is derived from the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

On the other hand, when the CAAC-OS film is analyzed by an in-planemethod in which an X-ray enters a sample in a direction perpendicular tothe c-axis, a peak appears frequently when 2θ is around 56°. This peakis derived from the (110) plane of the InGaZnO₄ crystal. Here, analysis(ϕ scan) is performed under conditions where the sample is rotatedaround a normal vector of a sample surface as an axis (ϕ axis) with 2θfixed at around 56°. In the case where the sample is a single-crystaloxide semiconductor film of InGaZnO₄, six peaks appear. The six peaksare derived from crystal planes equivalent to the (110) plane. On theother hand, in the case of a CAAC-OS film, a peak is not clearlyobserved even when ϕ scan is performed with 2θ fixed at around 56°.

According to the above results, in the CAAC-OS film having c-axisalignment, while the directions of a-axes and b-axes are differentbetween crystal parts, the c-axes are aligned in a direction parallel toa normal vector of a formation surface or a normal vector of a topsurface. Thus, each metal atom layer arranged in a layered mannerobserved in the cross-sectional TEM image corresponds to a planeparallel to the a-b plane of the crystal.

Note that the crystal part is formed concurrently with deposition of theCAAC-OS film or is formed through crystallization treatment such as heattreatment. As described above, the c-axis of the crystal is aligned witha direction parallel to a normal vector of a formation surface or anormal vector of a top surface. Thus, for example, in the case where ashape of the CAAC-OS film is changed by etching or the like, the c-axismight not be necessarily parallel to a normal vector of a formationsurface or a normal vector of a top surface of the CAAC-OS film.

Further, the degree of crystallinity in the CAAC-OS film is notnecessarily uniform. For example, in the case where crystal growthleading to the CAAC-OS film occurs from the vicinity of the top surfaceof the film, the degree of the crystallinity in the vicinity of the topsurface is higher than that in the vicinity of the formation surface insome cases. Further, when an impurity is added to the CAAC-OS film, thecrystallinity in a region to which the impurity is added is changed, andthe degree of crystallinity in the CAAC-OS film varies depends onregions.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed byan out-of-plane method, a peak of 2θ may also be observed at around 36°,in addition to the peak of 2θ at around 31°. The peak of 2θ at around36° indicates that a crystal having no c-axis alignment is included inpart of the CAAC-OS film. It is preferable that in the CAAC-OS film, apeak of 2θ appear at around 31° and a peak of 2θ do not appear at around36°.

With the use of the CAAC-OS film in a transistor, a change in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small. Thus, the transistor hashigh reliability.

Note that an oxide semiconductor film may be a stacked film includingtwo or more films of an amorphous oxide semiconductor film, amicrocrystalline oxide semiconductor film, and a CAAC-OS film, forexample.

For example, the CAAC-OS film is formed by a sputtering method with apolycrystalline oxide semiconductor sputtering target. When ions collidewith the sputtering target, a crystal region included in the sputteringtarget may be separated from the target along an a-b plane; in otherwords, a sputtered particle having a plane parallel to an a-b plane(flat-plate-like sputtered particle or pellet-like sputtered particle)may flake off from the sputtering target. In this case, theflat-plate-like sputtered particle or the pellet-like sputtered particlereaches a surface where the CAAC-OS film is to be deposited whilemaintaining its crystal state, whereby the CAAC-OS film can bedeposited.

The flat-plate-like sputtered particle has, for example, a diameter of acircle corresponding to a plane that is parallel to an a-b plane greaterthan or equal to 3 nm and less than or equal to 10 nm and a thickness(length in the direction perpendicular to the a-b plane) greater than orequal to 0.7 nm and less than 1 nm. Note that in the flat-plate-likesputtered particle, the plane parallel to the a-b plane may be a regulartriangle or a regular hexagon. Here, the term “equivalent circlediameter on a plane” refers to the diameter of a perfect circle havingthe same area as the plane.

For the deposition of the CAAC-OS film, the following conditions arepreferably used.

By increasing the substrate temperature during the deposition, migrationof a sputtered particle is likely to occur after the sputtered particlereaches a substrate surface. Specifically, the substrate temperatureduring the deposition is higher than or equal to 100° C. and lower thanor equal to 740° C., preferably higher than or equal to 200° C. andlower than or equal to 500° C. By increasing the substrate heatingtemperature during the deposition, when the flat-plate-like sputteredparticle reaches the substrate, migration occurs on the substrate, sothat a flat plane of the sputtered particle is attached to thesubstrate. At this time, the sputtered particle is charged positively,whereby sputtered particles are attached to the substrate whilerepelling each other; thus, the sputtered particles do not overlap witheach other randomly, and a CAAC-OS film with a uniform thickness can bedeposited.

By reducing the amount of impurities entering the CAAC-OS film duringthe deposition, the crystal state can be prevented from being broken bythe impurities. For example, the concentration of impurities (e.g.,hydrogen, water, carbon dioxide, or nitrogen) which exist in thedeposition chamber may be reduced. Furthermore, the concentration ofimpurities in a deposition gas may be reduced. Specifically, adeposition gas whose dew point is −80° C. or lower, preferably −100° C.or lower is used.

Furthermore, it is preferable that the proportion of oxygen in thedeposition gas be increased and the power be optimized in order toreduce plasma damage at the deposition. The proportion of oxygen in thedeposition gas is 30 vol. % or higher, preferably 100 vol. %.

After the CAAC-OS film is deposited, heat treatment may be performed.The temperature of the heat treatment is higher than or equal to 100° C.and lower than or equal to 740° C., preferably higher than or equal to200° C. and lower than or equal to 500° C. Further, the heat treatmentis performed for 1 minute to 24 hours, preferably 6 minutes to 4 hours.The heat treatment may be performed in an inert atmosphere or anoxidation atmosphere. It is preferable to perform heat treatment in aninert atmosphere and then to perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the CAAC-OS film for a short time. At thesame time, the heat treatment in an inert atmosphere may generate oxygenvacancies in the CAAC-OS film. In this case, the heat treatment in anoxidation atmosphere can reduce the oxygen vacancies. The heat treatmentcan further increase the crystallinity of the CAAC-OS film. Note thatthe heat treatment may be performed under a reduced pressure, such as1000 Pa or lower, 100 Pa or lower, 10 Pa or lower, or 1 Pa or lower. Theheat treatment under the reduced atmosphere can reduce the concentrationof impurities in the CAAC-OS film for a shorter time.

As an example of the sputtering target, an In—Ga—Zn—O compound target isdescribed below.

The In—Ga—Zn—O compound target, which is polycrystalline, is made bymixing InO_(X) powder, GaO_(Y) powder, and ZnO_(Z) powder in apredetermined molar ratio, applying pressure, and performing heattreatment at a temperature higher than or equal to 1000° C. and lowerthan or equal to 1500° C. Note that X, Y, and Z are each a givenpositive number. Here, the predetermined molar ratio of InO_(X) powderto GaO_(Y) powder and ZnO_(Z) powder is, for example, 1:1:1, 1:1:2,1:3:2, 2:1:3, 2:2:1, 3:1:1, 3:1:2, 3:1:4, 4:2:3, 8:4:3, or a ratio closeto these ratios. The kinds of powder and the molar ratio for mixingpowder may be determined as appropriate depending on the desiredsputtering target.

Alternatively, the CAAC-OS film is formed in the following manner.

First, a first oxide semiconductor film is formed to a thickness ofgreater than or equal to 1 nm and less than 10 nm. The oxidesemiconductor film is preferably formed by a sputtering method.Specifically, the substrate temperature during the deposition is higherthan or equal to 100° C. and lower than or equal to 500° C., preferablyhigher than or equal to 150° C. and lower than or equal to 450° C., andthe proportion of oxygen in the deposition gas is higher than or equalto 30 vol. %, preferably 100 vol. %.

Next, heat treatment is performed so that the first oxide semiconductorfilm serves as a first CAAC-OS film with high crystallinity. The heattreatment is performed at a temperature higher than or equal to 350° C.and lower than or equal to 740° C., preferably higher than or equal to450° C. and lower than or equal to 650° C. Further, the heat treatmentis performed for 1 minute to 24 hours, preferably 6 minutes to 4 hours.The heat treatment may be performed in an inert atmosphere or anoxidation atmosphere. It is preferable to perform heat treatment in aninert atmosphere and then to perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the first oxide semiconductor film for ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the first oxide semiconductor film. Inthis case, the heat treatment in an oxidation atmosphere can reduce theoxygen vacancies. Note that the heat treatment may be performed under areduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10 Pa orlower, or 1 Pa or lower. The heat treatment under the reduced atmospherecan reduce the concentration of impurities in the first oxidesemiconductor film for a shorter time.

The first oxide semiconductor film can be crystallized easier in thecase where the thickness is greater than or equal to 1 nm and less than10 nm than in the case where the thickness is greater than or equal to10 nm.

Next, a second oxide semiconductor film that has the same composition asthe first oxide semiconductor film is formed to a thickness of greaterthan or equal to 10 nm and less than or equal to 50 nm. The second oxidesemiconductor film is preferably formed by a sputtering method.Specifically, the substrate temperature during the deposition is higherthan or equal to 100° C. and lower than or equal to 500° C., preferablyhigher than or equal to 150° C. and lower than or equal to 450° C., andthe proportion of oxygen in the deposition gas is higher than or equalto 30 vol. %, preferably 100 vol. %.

Next, heat treatment is performed so that solid phase growth of thesecond oxide semiconductor film from the first CAAC-OS film isperformed. Thus, the second CAAC-OS film can have high crystallinity.The temperature of the heat treatment is higher than or equal to 350° C.and lower than or equal to 740° C., preferably higher than or equal to450° C. and lower than or equal to 650° C. Further, the heat treatmentis performed for 1 minute to 24 hours, preferably 6 minutes to 4 hours.The heat treatment may be performed in an inert atmosphere or anoxidation atmosphere. It is preferable to perform heat treatment in aninert atmosphere and then to perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the second oxide semiconductor film for ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the second oxide semiconductor film. Inthis case, the heat treatment in an oxidation atmosphere can reduce theoxygen vacancies. Note that the heat treatment may be performed under areduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10 Pa orlower, or 1 Pa or lower. The heat treatment under a reduced pressure canreduce the concentration of impurities in the second oxide semiconductorfilm in a shorter time.

In the above-described manner, a CAAC-OS film can be formed

Further, when the oxide semiconductor film contains a large amount ofhydrogen, the hydrogen and an oxide semiconductor are bonded to eachother, so that part of the hydrogen serves as a donor and causesgeneration of an electron which is a carrier. As a result, the thresholdvoltage of the transistor shifts in the negative direction. Accordingly,the concentration of hydrogen in the oxide semiconductor film ispreferably lower than 5×10¹⁸ atoms/cm³, more preferably lower than orequal to 1×10¹⁸ atoms/cm³, still more preferably lower than or equal to5×10¹⁷ atoms/cm³, further more preferably lower than or equal to 1×10¹⁶atoms/cm³. Note that the concentration of hydrogen in the oxidesemiconductor film is measured by secondary ion mass spectrometry(SIMS).

After formation of the oxide semiconductor film, it is preferable thatdehydration treatment (dehydrogenation treatment) be performed to removehydrogen or moisture from the oxide semiconductor film so that the oxidesemiconductor film is highly purified to contain impurities as little aspossible, and that oxygen be added to the oxide semiconductor film tofill oxygen vacancies increased by the dehydration treatment(dehydrogenation treatment). In this specification and the like,supplying oxygen to an oxide semiconductor film may be expressed asoxygen adding treatment, or treatment for making the oxygen content ofan oxide semiconductor film be in excess of that of the stoichiometriccomposition may be expressed as treatment for making an oxygen-excessstate.

In this manner, hydrogen or moisture is removed from the oxidesemiconductor film by dehydration treatment (dehydrogenation treatment)and oxygen vacancies therein are filled by oxygen adding treatment,whereby the oxide semiconductor film can be turned into an i-type(intrinsic) or substantially i-type oxide semiconductor film. The oxidesemiconductor film formed in such a manner includes extremely few (closeto zero) carriers derived from a donor, and the carrier concentrationthereof is lower than 1×10¹⁴/cm³, preferably lower than 1×10¹²/cm³,further preferably lower than 1×10¹¹/cm³, still further preferably lowerthan 1.45×10¹⁰/cm³.

The transistor including the oxide semiconductor layer which is highlypurified by sufficiently reducing the hydrogen concentration, and inwhich density of defect levels in the energy gap due to oxygen vacanciesare reduced by sufficiently supplying oxygen can achieve excellentoff-state current characteristics. For example, the off-state currentper micrometer in the channel width with a channel length of 1 μm atroom temperature (25° C.) is less than or equal to 100 yA (1 yA(yoctoampere) is 1×10⁻²⁴ A), desirably less than or equal to 10 yA. Inaddition, the off-state current per micrometer in the channel width at85° C. is less than or equal to 100 zA (1 zA (zeptoampere) is 1×10⁻²¹A), desirably less than or equal to 10 zA. In this manner, thetransistor which has extremely favorable off-state currentcharacteristics can be obtained with the use of an i-type (intrinsic) orsubstantially i-type oxide semiconductor layer.

Further, the oxide semiconductor film may have a structure in which aplurality of oxide semiconductor films is stacked.

For example, the oxide semiconductor film may be a stack of a firstoxide semiconductor film, a second oxide semiconductor film, and a thirdoxide semiconductor film which have different compositions.

Between the oxide semiconductor film (referred to as a first layer forconvenience) and a gate insulating film, a second layer which is formedof a constituent element of the first layer and whose electron affinityis lower than that of the first layer by 0.2 eV or more may be provided.At this time, when an electric field is applied from the gate electrode,a channel is formed in the first layer, and the channel is not formed inthe second layer. The element included in the first layer is the same asthat in the second layer; thus, interface scattering at the interfacebetween the first layer and the second layer hardly occurs. Thus,provision of the second layer between the first layer and the gateinsulating film can increase the field-effect mobility of thetransistor.

Further, when a silicon oxide film, a silicon oxynitride film, a siliconnitride oxide film, or a silicon nitride film is used as the gateinsulating film, silicon included in the gate insulating film may bemixed into the oxide semiconductor film. When silicon is included in theoxide semiconductor film, a decrease in crystallinity of the oxidesemiconductor film, a decrease in carrier mobility, or the like occurs.Thus, the second layer is preferably provided between the first layerand the gate insulating film so that the concentration of silicon in thefirst layer where a channel is formed is reduced. For the same reason,it is preferable that a third layer which is formed of the constituentelement of the first layer and whose electron affinity is lower thanthat of the first layer by 0.2 eV or more be provided and that the firstlayer be sandwiched between the second layer and the third layer.

The methods and structures described in this embodiment can be combinedas appropriate with any of the methods and structures described in theother embodiments.

Embodiment 4

In this embodiment, an example of a semiconductor device (also referredto as a display device) having a display function which is manufacturedusing the manufacturing apparatus described in Embodiment 1 isdescribed.

FIG. 8A is a plan view of a display device of this embodiment. In FIG.8A, a sealant 4005 is provided so as to surround a pixel portion 4002and a scan line driver circuit 4004 which are provided over a substrate4001. A substrate 4006 is provided over the pixel portion 4002 and thescan line driver circuit 4004. Consequently, the pixel portion 4002 andthe scan line driver circuit 4004 are sealed together with a displayelement by the substrate 4001, the sealant 4005, and the substrate 4006.In FIG. 8A, an IC chip is mounted on a region of the substrate 4001,which is different from the region surrounded by the sealant 4005;alternatively, a signal line driver circuit 4003 which is formed using asingle crystal semiconductor film or a polycrystalline semiconductorfilm is formed over a substrate separately prepared. A variety ofsignals and potentials which are provided for the pixel portion 4002through the signal line driver circuit 4003 and the scan line drivercircuit 4004 are supplied from a flexible printed circuit (FPC) 4018.

Although FIG. 8A illustrates an example in which the signal line drivercircuit 4003 is formed separately and mounted on the first substrate4001, the present invention is not limited to this structure. The scanline driver circuit may be separately formed and then mounted, or onlypart of the signal line driver circuit or part of the scan line drivercircuit may be separately formed and then mounted.

Note that a connection method of a separately formed driver circuit isnot particularly limited, and a chip on glass (COG) method, a wirebonding method, a tape automated bonding (TAB) method, or the like canbe used. FIG. 8A illustrates an example in which the signal line drivercircuit 4003 is mounted by a COG method.

Note that the display device includes a panel in which the displayelement is sealed, and a module in which an IC including a controller orthe like is mounted on the panel. In other words, the display device inthis specification means an image display device or a light source(including a lighting device). Furthermore, the display device alsoincludes the following modules in its category: a module to which aconnector such as an FPC or a Tape Carrier Package (TCP) is attached; amodule having a TCP at the tip of which a printed wiring board isprovided; and a module in which an integrated circuit (IC) is directlymounted on a display element by a COG method.

The pixel portion and the scan line driver circuit provided over thesubstrate include a plurality of transistors, and the transistordescribed in Embodiment 2 can be applied thereto.

A liquid crystal element (also referred to as a liquid crystal displayelement) or a light-emitting element (also referred to as alight-emitting display element) can be used as the display elementprovided in the display device. The light-emitting element includes anelement whose luminance is controlled by current or voltage in itscategory, and specifically includes an inorganic electroluminescent (EL)element, an organic EL element, and the like. Furthermore, a displaymedium whose contrast is changed by an electric effect, such as anelectronic ink display device (electronic paper), can be used.

FIG. 8C is a cross-sectional view taken along line M-N in FIG. 8A. Anexample of a liquid crystal display device using a liquid crystalelement as a display element is shown in FIG. 8C. Note that a transistor4010 provided in the pixel portion 4002 is electrically connected to adisplay element to form a display panel. A variety of display elementscan be used as the display element as long as display can be performed.

A liquid crystal display device can employ a vertical electric fieldmode or a horizontal electric field mode. FIG. 8C illustrates an examplein which a fringe field switching (FFS) mode is employed.

As illustrated in FIGS. 8A and 8C, the semiconductor device includes aconnection terminal electrode 4015 and a terminal electrode 4016. Theconnection terminal electrode 4015 and the terminal electrode 4016 areelectrically connected to a terminal included in the FPC 4018 through ananisotropic conductive layer 4019.

The connection terminal electrode 4015 is formed from the sameconductive layer as a first electrode layer 4034. The terminal electrode4016 is formed from the same conductive layer as gate electrode layersof the transistor 4010 and a transistor 4011.

A plurality of thin film transistors are included in a pixel portion4002 and a scan line driver circuit 4004 which are formed over the firstsubstrate 4001. FIG. 8C illustrates the transistor 4010 included in thepixel portion 4002 and the transistor 4011 included in the scan linedriver circuit 4004, and insulating layers 4032 a and 4032 b areprovided over the transistors 4010 and 4011.

In FIG. 8C, a planarization insulating layer 4040 is provided over theinsulating layer 4032 b, and an insulating layer 4042 is providedbetween the first electrode layer 4034 and a second electrode layer4031.

The transistor including an oxide semiconductor in a channel formationregion which is described in Embodiment 2 can be used for each of thetransistors 4010 and 4011. The transistors 4010 and 4011 are bottom-gatetransistors.

A gate insulating layer included in the transistors 4010 and 4011 canhave a single layer structure or a stacked structure. In thisembodiment, the gate insulating layer may have a stacked structureincluding a gate insulating layers 4020 a and 4020 b. In FIG. 8C, thegate insulating layer 4020 a and the insulating layer 4032 b extendbelow the sealant 4005 to cover the end portion of the connectionterminal electrode 4015, and the insulating layer 4032 b covers sidesurfaces of the gate insulating layer 4020 b and the insulating layer4032 a.

Moreover, a conductive layer may be provided so as to overlap with achannel formation region of the oxide semiconductor layer of thetransistor 4011 for the driver circuit. The conductive layer is providedat the position overlapping with the channel formation region of theoxide semiconductor layer, whereby the amount of shift in thresholdvoltage of the transistor 4011 can be reduced.

The conductive layer also has a function of blocking an externalelectric field, that is, to prevent an external electric field(particularly, to prevent static electricity) from effecting the inside(a circuit portion including a transistor). The blocking function of theconductive layer can prevent a change in the electrical characteristicsof the transistor due to the effect of the external electric field suchas static electricity.

Here, the planarization insulating layer 4040 corresponds to the organicresin film described in Embodiment 1. The planarization insulating layer4040 can be formed using an organic resin such as, an acrylic resin, apolyimide resin, a benzocyclobutene-based resin, a polyamide resin, oran epoxy resin. Other than such organic materials, a low-dielectricconstant material (a low-k material) or a siloxane-based resin can beused. By application of the method described in Embodiment 1, impuritiessuch as water in the planarization insulating layer 4040 is extremelyreduced. Thus, a change in the electrical characteristics of thetransistor is suppressed, and a significantly reliable display devicecan be realized.

In FIG. 8C, a liquid crystal element 4013 includes the first electrodelayer 4034, the second electrode layer 4031, and a liquid crystal layer4008. Note that insulating layers 4033 and 4038 functioning as alignmentfilms are provided so that the liquid crystal layer 4008 is interposedtherebetween.

In the liquid crystal element 4013, the second electrode layer 4031having an opening pattern is provided below the liquid crystal layer4008, and the first electrode layer 4034 having a flat plate shape isprovided below the second electrode layer 4031 with the insulating layer4042 provided therebetween. The second electrode layer 4031 having anopening pattern includes a bent portion or a branched comb-shapedportion. The provision of the opening pattern for the second electrodelayer 4031 enables an electric field to be generated between electrodesof the first electrode layer 4034 and the second electrode layer 4031.Note that a structure may be employed in which the second electrodelayer 4031 having a flat plate shape is formed on and in contact withthe planarization insulating layer 4040, and the first electrode layer4034 having an opening pattern and serving as a pixel electrode isformed over the second electrode layer 4031 with the insulating layer4042 provided therebetween.

The first electrode layer 4034 and the second electrode layer 4031 canbe formed using a light-transmitting conductive material such as indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, indium tin oxide, indium zinc oxide, indiumtin oxide to which silicon oxide is added, or graphene.

Alternatively, the first electrode layer 4034 and the second electrodelayer 4031 can be formed using one or more materials selected frommetals such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium(Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt(Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper(Cu), and silver (Ag); an alloy of any of these metals; and a nitride ofany of these metals.

A conductive composition containing a conductive high molecule (alsoreferred to as a conductive polymer) can be used for the first electrodelayer 4034 and the second electrode layer 4031.

A columnar spacer denoted by reference numeral 4035 is obtained byselective etching of an insulating layer and is provided in order tocontrol the thickness of the liquid crystal layer 4008 (a cell gap).Alternatively, a spherical spacer may be used.

Alternatively, a liquid crystal composition exhibiting a blue phase forwhich an alignment film is unnecessary may be used for the liquidcrystal layer 4008. In this case, the liquid crystal layer 4008 is incontact with the first electrode layer 4034 and the second electrodelayer 4031.

In the liquid crystal display device of this embodiment illustrated inFIG. 8C, the substrate 4001 provided with the transistors 4010 and 4011,the insulating layers 4032 a and 4032 b, the planarization insulatinglayer 4040, the first electrode layer 4034, the insulating layer 4042,the second electrode layer 4031, and the insulating layer 4038functioning as an alignment film corresponds to the first substrate 100in Embodiment 1. Further, the substrate 4006 provided with the spacer4035 and the insulating layer 4033 functioning as an alignment filmcorresponds to the second substrate 200 in Embodiment 1. The liquidcrystal display device of this embodiment can be formed in such a mannerthat the insulating layers 4038 and 4033 functioning as alignment filmsare formed over the substrates 4001 and 4006, respectively, rubbingtreatment and cleaning after the rubbing treatment are performed, andthen bonding using the manufacturing apparatus of one embodiment of thepresent invention is performed.

The substrates 4001 and 4006 are bonded to each other using themanufacturing apparatus described in Embodiment 1, so that moistureincluded in the planarization insulating layer 4040 can be removed andentry of water can be prevented. Because in the liquid crystal displaydevice of this embodiment, moisture in the display device is reduced, ahighly reliable liquid crystal display device in which a change in theelectrical characteristics of the transistors 4010 and 4011 issuppressed can be obtained.

Note that the insulating layer 4042 illustrated in FIG. 8C partly has anopening; thus, moisture included in the planarization insulating layer4040 can be released through the opening. However, the opening is notnecessarily provided depending on the quality of the insulating layer4042 over the planarization insulating layer 4040.

The size of storage capacitor formed in the liquid crystal displaydevice is set considering the leakage current of the transistor providedin the pixel portion or the like so that charge can be held for apredetermined period. The size of the storage capacitor may be setconsidering the off-state current of a transistor or the like. By usinga transistor including the oxide semiconductor layer disclosed in thisspecification, the size of the storage capacitor can be reduced.Accordingly, the aperture ratio of each pixel can be improved.

In particular, it is preferable that a capacitor as a storage capacitorbe not provided and that parasitic capacitance generated between thefirst electrode layer 4034 and the second electrode layer 4031 be usedas a storage capacitor. Without the capacitor, the aperture ratio of apixel can be further increased.

FIG. 8B illustrates an example of a pixel structure in the case wherethe capacitor as a storage capacitor is not provided for a pixel. Thepixel has an intersection portion of a wiring 4050 electricallyconnected to the gate electrode layer of the transistor 4010 and awiring 4052 electrically connected to one of a source electrode layerand a drain electrode layer of the transistor 4010. Since the pixel inFIG. 8B does not include the capacitor as a storage capacitor, the ratioof the area of the second electrode layer 4031 having an opening patternto the area occupied by the pixel can be made large, and an extremelyhigh aperture ratio can be obtained.

In the transistor including an oxide semiconductor layer, which isdisclosed in this specification, the current in an off state (off-statecurrent) can be made small. Accordingly, an electric signal such asimage data can be held for a longer period and a writing interval can beset longer. Accordingly, frequency of refresh operation can be reduced,which leads to an effect of suppressing power consumption.

The transistor including an oxide semiconductor layer, which isdisclosed in this specification, can have high field-effect mobility;thus, the transistor can operate at high speed. For example, when such atransistor is used for a liquid crystal display device, a switchingtransistor in a pixel portion and a driver transistor in a drivercircuit portion can be formed over one substrate. In addition, by usingsuch a transistor in a pixel portion, a high-quality image can beprovided.

In the display device, a black matrix (a light-blocking layer), anoptical member (an optical substrate) such as a polarizing member, aretardation member, or an anti-reflection member, and the like areprovided as appropriate. For example, circular polarization by apolarizing plate and a retardation plate may be used. In addition, abacklight, a side light, or the like may be used as a light source.

As a display method in the pixel portion, a progressive method, aninterlace method or the like can be employed. Further, color elementscontrolled in a pixel at the time of color display are not limited tothree colors: R, G, and B (R, G, and B correspond to red, green, andblue, respectively). For example, R, G, B, and W (W corresponds towhite); R, G, B, and one or more of yellow, cyan, magenta, and the like;or the like can be used. Further, the sizes of display regions may bedifferent between respective dots of color elements. Note that thedisclosed invention is not limited to the application to a displaydevice for color display; the disclosed invention can also be applied toa display device for monochrome display.

In addition, the display device is preferably provided with a touchsensor. More intuitively operable electronic devices can be eachobtained by using a display device with a touch sensor for an electronicdevice or the like so that the display device overlaps with the pixelportion 4002.

As the touch sensor provided for the display device, a capacitive touchsensor is preferably used. In addition, a variety of types such as aresistive type, a surface acoustic wave type, an infrared type, and anoptical type can be used.

Examples of the capacitive touch sensor are typically of a surfacecapacitive type, a projected capacitive type, and the like. Further,examples of the projected capacitive type are of a self capacitive type,a mutual capacitive type, and the like mainly in accordance with thedifference in the driving method. The use of a mutual capacitive type ispreferable because multiple points can be sensed simultaneously.

When a touch sensor is provided for the display device, a layerfunctioning as a touch sensor can be arranged in various ways.

FIGS. 9A to 9C each illustrate a structural example of a display deviceincluding a liquid crystal element and a touch sensor.

The display device in FIG. 9A includes a liquid crystal 4062, a pair ofsubstrates (substrates 4061 and 4063) provided with the liquid crystal4062 therebetween, a pair of polarizing plates (polarizing plates 4064and 4065) provided outside the substrates 4061 and 4063, and a touchsensor 4060. Here, a structure including the liquid crystal 4062 and thesubstrates 4061 and 4063 are referred to as a display panel 4067.

The display device in FIG. 9A is a so-called external display device inwhich the touch sensor 4060 is placed outside the polarizing plate 4064(or the polarizing plate 4065). With such a structure, the displaydevice can have a touch sensor function in such a manner that thedisplay panel 4067 and the touch sensor 4060 are separately formed andthen they are overlapped with each other. Thus, the display device inFIG. 9A can be easily manufactured without a special step.

The display device in FIG. 9B is a so-called on-cell display device inwhich the touch sensor 4060 is positioned between the polarizing plate4064 and the substrate 4061 (or between the polarizing plate 4065 andthe substrate 4063). With such a structure, the thickness of the displaydevice can be reduced by using the substrate 4061 in common with aformation substrate of the touch sensor 4060, for example.

The display device in FIG. 9C is a so-called in-cell display device inwhich the touch sensor 4060 is positioned between the substrate 4061 andthe substrate 4063. With such a structure, the thickness of the displaydevice can be further reduced. For example, this can be realized in sucha manner that a layer functioning as a touch sensor is formed on theliquid crystal 4062 side of a surface of the substrate 4061 (or thesubstrate 4063) with the use of a transistor, a wiring, an electrode,and the like included in the display panel 4067. Further, in the case ofusing an optical touch sensor, a structure provided with a photoelectricconversion element may be employed.

Note that the display device including a liquid crystal element isdescribed here; however, a function of a touch sensor can be properlyadded to various display devices such as a display device provided withan organic EL element and electronic paper.

The methods and structures described in this embodiment can be combinedas appropriate with any of the methods and structures described in theother embodiments.

Embodiment 5

In this embodiment, examples of an electronic device provided with adisplay device manufactured using a manufacturing apparatus of oneembodiment of the present invention is described with reference to FIGS.10A to 10F.

The electronic device illustrated in FIG. 10A is an example of afoldable information terminal.

The electronic device illustrated in FIG. 10A has a housing 1021 a, ahousing 1021 b, a panel 1022 a provided for the housing 1021 a, a panel1022 b provided for the housing 1021 b, a hinge 1023, a button 1024, aconnection terminal 1025, a recording medium insertion portion 1026, anda speaker 1027.

The housing 1021 a and the housing 1021 b are connected by the hinge1023.

Since the electronic device in FIG. 10A includes the hinge 1023, it canbe folded so that the panels 1022 a and 1022 b face each other.

The button 1024 is provided for the housing 1021 b. Note that thehousing 1021 a may also be provided with the button 1024. For example,when the button 1024 which functions as a power button is provided andpushed, supply of a power voltage to the electronic device can becontrolled.

The connection terminal 1025 is provided for the housing 1021 a. Notethat the connection terminal 1025 may be provided on the housing 1021 b.Alternatively, a plurality of connection terminals 1025 may be providedon one or both of the housings 1021 a and 1021 b. The connectionterminal 1025 is a terminal for connecting the electronic deviceillustrated in FIG. 10A to another device.

The recording medium insertion portion 1026 is provided in the housing1021 a. The recording medium insertion portion 1026 may be provided inthe housing 1021 b. Alternatively, a plurality of recording mediuminsertion portions 1026 may be provided in one or both of the housings1021 a and 1021 b. For example, a card-type recording medium is insertedinto the recording medium insertion portion so that data can be read tothe electronic device from the card-type recording medium or data storedin the electronic device can be written to the card-type recordingmedium.

The speaker 1027 is provided on the housing 1021 b. The speaker 1027outputs sound. Note that the speaker 1027 may be provided on the housing1021 a.

Note that the housing 1021 a or the housing 1021 b may be provided witha microphone, in which case the electronic device in FIG. 10A canfunction as a telephone, for example

The electronic device illustrated in FIG. 10A functions as one or moreof a telephone set, an e-book reader, a personal computer, and a gamemachine, for example.

In the panels 1022 a and/or the panel 1022 b, the display devicemanufactured using a manufacturing apparatus of one embodiment of thepresent invention can be used.

An electronic device in FIG. 10B is an example of a stationaryinformation terminal. The electronic device illustrated in FIG. 10Bincludes a housing 1031, a panel 1032 provided in the housing 1031, abutton 1033, and a speaker 1034.

Note that a panel similar to the panel 1032 may be provided for a deckportion 1035 of the housing 1031.

The housing 1031 may be provided with one or more of a ticket slot fromwhich a ticket or the like is dispensed, a coin slot, and a bill slot.

The button 1033 is provided for the housing 1031. For example, when thebutton 1033 is a power button, supply of a power voltage to theelectronic device can be controlled by pressing the button 1033.

The speaker 1034 is provided for the housing 1031. The speaker 1034outputs sound.

The electronic device illustrated in FIG. 10B functions as, for example,an automated teller machine, an information communication terminal forordering a ticket or the like (also referred to as a multi-mediastation), or a game machine.

In the panel 1032, the display device manufactured using a manufacturingapparatus of one embodiment of the present invention can be used.

FIG. 10C illustrates an example of a stationary information terminal.The electronic device in FIG. 10C has a housing 1041 provided with apanel 1042, a support 1043 for supporting the housing 1041, a button1044, a connection terminal 1045, and a speaker 1046.

Note that a connection terminal for connecting the housing 1041 to anexternal device may be provided.

The button 1044 is provided for the housing 1041. For example, when thebutton 1044 is a power button, supply of a power voltage to theelectronic device can be controlled by pressing the button 1044.

The connection terminal 1045 is provided for the housing 1041. Theconnection terminal 1045 is a terminal for connecting the electronicdevice illustrated in FIG. 10C to another device. For example,connecting the electronic device illustrated in FIG. 10C and a personalcomputer with the connection terminal 1045 enables the panel 1042 todisplay an image corresponding to a data signal input from the personalcomputer. For example, when the panel 1042 of the electronic device inFIG. 10C is larger than a panel of another electronic device connectedthereto, a displayed image of the another electronic device can beenlarged, so that a plurality of viewers can easily see the image at thesame time.

The speaker 1046 is provided on the housing 1041. The speaker 1046outputs sound.

The electronic device in FIG. 10C functions as at least one of an outputmonitor, a personal computer, and a television set, for example.

In the panel 1042, the display device manufactured using a manufacturingapparatus of one embodiment of the present invention can be used.

The electronic devices illustrated in FIGS. 10D and 10E are examples ofa portable information terminal.

A portable information terminal 1010 illustrated in FIG. 10D is providedwith, in addition to a panel 1012A incorporated in a housing 1011,operation buttons 1013, and a speaker 1014. Further, although not shown,the portable information terminal 1010 includes a microphone, anexternal connection port such as a stereo headphone jack, an insertionport for a memory card, a camera, or a USB connector, and the like.

Here, the display device manufactured using a manufacturing apparatus ofone embodiment of the present invention can be used for the panel 1012A.

A portable information terminal 1020 illustrated in FIG. 10E is providedwith a panel 1012B that is curved along the side surface of the housing1011. A portable information terminal including a panel with a curvedsurface can be obtained by the use of a substrate with a curved surfaceas a support substrate of a touch sensor and a display element.

A portable information terminal 1020 illustrated in FIG. 10E is providedwith, in addition to a display portion 1012B incorporated in the housing1011, operation buttons 1013, a speaker 1014, a microphone 1015, anexternal connection port which is not shown such as a stereo headphonejack, an insertion port for a memory card, a camera, or a USB connector,and the like.

The portable information terminals illustrated in FIGS. 10D and 10E eachhas a function of one or more of a telephone set, an e-book reader, apersonal computer, and a game machine.

The electronic device illustrated in FIG. 10F is an example of afoldable information terminal.

The electronic device 1050 illustrated in FIG. 10F has a housing 1051, ahousing 1052, a panel 1054 provided for the housing 1051, a panel 1055provided for the housing 1052, a speaker 1056, a start button 1057, anda connection terminal 1025.

In the electronic device 1050 illustrated in FIG. 10F, the housing 1051and the housing 1052 are connected to each other using a hinge 1053 andcan be folded.

A display device manufactured using a manufacturing apparatus of oneembodiment of the present invention can be used for at least one of thepanel 1054 and the panel 1055.

As described with reference to FIGS. 10A to 10F, a display device of oneembodiment of the present invention is used for a panel of an electronicdevice of this embodiment. The display device has high reliability;thus, the electronic device can have high reliability.

The methods and structures described in this embodiment can be combinedas appropriate with any of the methods and structures described in theother embodiments.

Example 1

In this example, a liquid crystal display device (liquid crystal panel)manufactured through a cell process using the manufacturing apparatus ofone embodiment of the present invention described in Embodiment 1 isdescribed together with a comparative example, and effects of drytreatment and atmosphere control are described.

In this example, a change in operating margin of a scan line drivercircuit included in the liquid crystal panel over time was measured.Liquid crystal panels H and I, whose changes in operating margin overtime were measured, are liquid crystal panels which were manufactured inthe same process up to and including the step of forming an alignmentfilm. In each of the liquid crystal panels H and I, a scan line drivercircuit is formed over the same substrate as a pixel, and a 3 μm-thickorganic resin film containing an acrylic resin is formed over atransistor included in the scan line driver circuit. Further, a channelformation region of the transistor is formed using an oxidesemiconductor layer.

The liquid crystal panel H is a liquid crystal panel manufactured usingthe manufacturing apparatus of one embodiment of the present invention.FIG. 13 illustrates the manufacturing apparatus of one embodiment of thepresent invention which was used for manufacture of the liquid crystalpanel H. In FIG. 13, an arrow indicates a movement path of a substrate,and the number surrounded by a circle indicates the order of steps.

The liquid crystal panel H was manufactured in the following manner. Afirst substrate provided with an organic resin film and an alignmentfilm over a transistor including an oxide semiconductor was prepared,the first substrate of which the alignment film had been baked andsubjected to rubbing treatment was carried into a first heat treatmentchamber, and heat treatment was performed at 160° C. for one hour in areduced pressure atmosphere of 10⁻⁵ Pa. After being subjected to theheat treatment, the first substrate was transferred to a bonding chamberand arranged on a second stage.

Further, a second substrate of which an alignment film had been formed,baked, and subjected to rubbing treatment was carried into a second heattreatment chamber, and heat treatment was performed at 160° C. for onehour in a reduced pressure atmosphere of 10⁻⁵ Pa. After that, the secondsubstrate was carried into an application chamber, a sealant was appliedin a frame shape, and then a liquid crystal was dropped inside thesealant in a frame shape.

After the drop of the liquid crystal, the second substrate wastransferred to a bonding chamber and mounted on a first stage, wherebythe second substrate and the first substrate were bonded to each other.The bonding was performed in a reduced pressure atmosphere of 100 Pa.After that, UV lamp irradiation was performed in a curing chamber tocure the sealant. Thus, the liquid crystal panel H in which a liquidcrystal layer was sealed between the substrates was manufactured.

On the other hand, the liquid crystal panel I was manufactured in thefollowing manner. After formation of the alignment film on each of thefirst substrate and the second substrate, heat treatment was performedat 150° C. for six hours in an air atmosphere. After that, a sealant wasdrawn on one of the substrates, a liquid crystal material was dropped ina region surrounded by the sealant, and the substrates were bonded toeach other in a reduced pressure atmosphere. Thus, the liquid crystalpanel I in which a liquid crystal layer was sealed between thesubstrates was manufactured.

An operating margin width (V) of the scan line driver circuit includedin each of the liquid crystal panels H and I was examined in such amanner that a start pulse signal and a clock signal were input to a959-stage sequential circuit included in a shift register of the scanline driver circuit, and a waveform of a signal thereby output from thelast stage of the sequential circuit was observed using an oscilloscope.

As the start pulse signal, a signal having a pulse with a 68.3 μsecwidth which successively appears, with a frequency of 60 Hz, was used.Further, in each of the clock signal and the start pulse signal, a lowvoltage GVSS was −14 V. The value of high voltage GVDD where thewaveform of a signal output from the last stage of the sequentialcircuit was disordered when a high voltage GVDD of each of the clocksignal and the start pulse signal was gradually decreased from +14 V isdefined as a voltage at which a malfunction occurs. Further, thedifference between +14 V that is the highest voltage GVDD and themalfunction voltage is defined as an operating margin width.

FIG. 11 illustrates the change in an operating margin width (V) withrespect to an operation time (hour) in the scan line driver circuitincluded in the liquid crystal panel H. Further, FIG. 12 illustrates thechange in an operating margin width (V) with respect to an operationtime (hour) in the scan line driver circuit included in the liquidcrystal panel I.

From FIG. 11 and FIG. 12, the operating margin widths of the liquidcrystal panels H and I were the same, about 22 V, at the start of theoperation; however, after 220 hours, the operating margin width of theliquid crystal panel H was about 17 V, and the operating margin width ofthe liquid crystal panel I was about 7 V. Thus, the operating marginwidth of the liquid crystal panel I was decreased in a shorter time thanthat of the liquid crystal panel H. Therefore, it is recognized that theamount of shift in the threshold voltage of the transistor included inthe scan line driver circuit of the liquid crystal panel H is smallerthan that of the liquid crystal panel I.

This shows that the liquid crystal display device manufactured using themanufacturing apparatus of one embodiment of the present invention is ahighly reliable liquid crystal display device.

This application is based on Japanese Patent Application serial no.2012-226893 filed with Japan Patent Office on Oct. 12, 2012, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A method for manufacturing a display device,comprising: heating a first substrate with a transistor; heating asecond substrate with an organic material containing an organic resin;applying a sealing material to a surface of one of the first and secondsubstrates; attaching the first and second substrates with the sealingmaterial therebetween; and curing the sealing material, wherein: each ofthe heating steps is performed in a reduced pressure atmosphere or aninert gas atmosphere, and from the heating steps to the attaching step,the first and second substrates are processed without exposure to theair.
 2. The method according to claim 1, wherein in each of the heatingsteps, the first and second substrates are processed in different heattreatment chambers, respectively.
 3. The method according to claim 1,wherein the attaching step is performed in a reduced pressureatmosphere.
 4. The method according to claim 1, wherein a channelformation region of the transistor includes an oxide semiconductor. 5.The method according to claim 1, wherein the sealing material serves asa solid sealing.
 6. The method according to claim 1, wherein from theheating steps to the attaching step, the first and second substrates areprocessed in an atmosphere with a dew point of −60° C. or lower.
 7. Themethod according to claim 1, wherein the curing step is performedthrough light irradiation.
 8. A method for manufacturing a displaydevice, comprising: heating a first substrate with a transistor; heatinga second substrate with an organic material; applying a sealing materialto a surface of one of the first and second substrates; attaching thefirst and second substrates with the sealing material therebetween;pre-curing the sealing material; and curing the sealing material,wherein: each of the heating steps is performed in a reduced pressureatmosphere or an inert gas atmosphere, from the heating steps to theattaching step, the first and second substrates are processed withoutexposure to the air, and the attaching step and the pre-curing step areperformed in the same treatment chamber.
 9. The method according toclaim 8, wherein in each of the heating steps, the first and secondsubstrates are processed in different heat treatment chambers,respectively.
 10. The method according to claim 8, wherein the attachingstep is performed in a reduced pressure atmosphere.
 11. The methodaccording to claim 8, wherein a channel formation region of thetransistor includes an oxide semiconductor.
 12. The method according toclaim 8, wherein the sealing material serves as a solid sealing.
 13. Themethod according to claim 8, wherein the organic material contains anorganic resin.
 14. The method according to claim 8, wherein from theheating steps to the attaching step, the first and second substrates areprocessed in an atmosphere with a dew point of −60° C. or lower.
 15. Themethod according to claim 8, wherein the curing step is performedthrough light irradiation.
 16. The method according to claim 8, whereinthe pre-curing step is performed through light irradiation or heattreatment.